Atrial fibrillation (AF) is the most common arrhythmia and affects over 3 million Americans, a number that is expected to rise to 12 million in 2050. AF is a major public health burden as it is associated with a five-fold increased stroke risk, doubling in dementia risk, tripling in heart failure risk, and nearly two-fold increase in mortality. Many risk factors for AF have been identified, including advancing age, male sex, hypertension, heart failure, obesity and family history. Despite the profound socioeconomic costs of AF, our understanding of the fundamental mechanisms for the arrhythmia remains largely unknown. The central goal of the candidate's research work is to use genetics to identify novel genes and pathways for AF. The candidate is a cardiac electrophysiologist with a research focus on atrial fibrillation. He has developed a cohort of patients with lone atrial fibrillation, leads an international consortium of investigators studying the genetics of atrial fibrillation, and performs laboratory work on the mechanisms of AF. Despite the initial success that candidate has had in developing a program in arrhythmia research, his clinical commitments had limited his exposure to the increasing number of fellows that he was mentoring. In 2010, the candidate received a K24 award entitled ?Mentoring in Arrhythmia Research? that enable him to reduce his clinical time and focus on mentoring of his trainees. The time afforded by this award was transformative in the candidate's research program and his academic success. Therefore, the specific aims of this competitive renewal are to provide the candidate long-term support to enable a continued reduction in his clinical commitments, and to expand the research training of fellows interested patient-oriented research in atrial fibrillation and electrophysiology. Research fellows will have ample opportunities to participate in patient-oriented research through in the MGH AF study, the AFGen Consortium, and the candidates own translational laboratory work. These research opportunities will be complemented by the extensive educational resources available at Massachusetts General Hospital, the Broad Institute, and Harvard University. Ultimately, we hope that this proposal will contribute to the development of new clinical investigators in arrhythmia research and to further our understanding of this common and morbid arrhythmia.